Per Mertesacker has offered a candid and damning assessment of Arsenal’s shortcomings this season, saying that the intricate passing game is misfiring, there are issues at the back and the collective confidence is low. The centre-half also admitted that he is struggling to refocus on a personal level after his exertions for Germany in their World Cup triumph.

Arsenal dodged a bullet at Anderlecht on Wednesday night, when they scored twice in the last minute to sneak a fortunate 2-1 win that kept them on course to qualify from Champions League Group D. But the team’s problems were clear, with arguably the most worrying being the poor quality of their passing.

They were extremely narrow in midfield, possibly because the wide players, Alexis Sánchez and Santi Cazorla, have the natural inclination to drift inside and those one-twos into the penalty area are not coming off. Mertesacker knows that there has to be an improvement at Sunderland in the Premier League on Saturday.

“Football-wise, we lack a few things,” Mertesacker said. “The passing game is not as efficient as last year. We are not at our best, we have to admit that. We have to be honest to ourselves and train harder.

“Again, it is away from home on Saturday and again, I think we have to do better with our possession – to put more pressure on them, not to lose so many balls in the middle of the park, to play more in wide areas. I think it is better to expose them there, instead of playing one-twos through the middle. It doesn’t work as much as last season, so we have to work on that.

“To sum it up, the last five minutes [against Anderlecht] were great; the 85 minutes before, we lacked a bit of everything. We are just pleased with the last five minutes and our finishing. I feel sorry for them, because they did nearly everything. But they just suffered in the last five minutes and added time.”

Arsène Wenger, the manager, was forced to partner Mertesacker in central defence with Nacho Monreal, the left-back, as his lack of depth at the back has been exposed by injuries. Laurent Koscielny, the centre-half, is out with tendinitis in an achilles and he needs rest, ideally for another month. Wenger would like to hold him back until the home league fixture against Manchester United on 22 November. After Sunderland, Arsenal face Burnley and Anderlecht at home, and Swansea City away. Mathieu Debuchy, the right-back, is a long-term casualty with ankle damage.

The team was guilty of their latest defensive switch-off against Anderlecht, when Dennis Praet was allowed to cross from the right and Andy Najar eluded what passed for the marking to head home in the 71st minute. Calum Chambers, the right-back, had to be tighter to Najar.

Mertesacker was asked whether he was finding it difficult to hold the back four together. “It is difficult,” he replied. “For me personally, it is difficult at the moment because that was really a long season last year, and to come back from the World Cup and get the motivation back – I am nearly back but you can feel there is something missing at the moment.

“Those who come in [to central defence] do a fantastic job and that is vital for the belief and for the character of the team. Nacho Monreal is not a natural centre-back but he tries hard, and he puts everything in it, and everyone can see it.”

Mertesacker painted the picture of a team that is groping for the solutions. “We came back [to win],” he said. “There was a bit of belief but not that belief. So it was a bit strange. Everyone knows that it is a difficult start to the season for us, and confidence is not that much how we want it. But the character is good and the mentality is good.”

Arsenal boast three Germany World Cup winners, and all three have suffered hang-overs from Brazil. Mesut Özil is out until December with ankle ligament damage – an injury that Wenger says was linked to his efforts at the World Cup – while Lukas Podolski has been caught in the vicious circle of lacking full fitness and, in turn, not being selected and failing to develop rhythm and sharpness.

Podolski came on as an 83rd-minute substitute against Anderlecht for his latest brief appearance of the club season – his Arsenal minutes so far add up to 146 – but he got himself into the right place to turn home the last-gasp winner.

“He is in a difficult period but [showed]how vital he is,” Mertesacker said. “He showed with his clinical finish. You can wake him up any second in the day and he will score with his left foot. I would say he’s the best finisher I’ve played with. You can see that every day in training. Even with the side of his foot, he has power. We play a lot of football around the box but when it comes to finishing and shooting, we lack that. So he gives us another quality.”

Wenger gave the Germany players a month off after the World Cup final and it meant that they began their pre-season work on 11 August – the day after the club had beaten Manchester City in the Community Shield. Mertesacker is now retired from international football.

“We had already won the Community Shield and we weren’t there,” Mertesacker said. “We were still on holiday, and that was something really strange for us to think about. We didn’t even have time to celebrate [the World Cup win] properly. We came back to Berlin, got on the stage, waved our hands, showed the World Cup and then everybody disappeared to their family to get some holidays. But it was very difficult to get into a proper holiday. The re-start is even more in your head than anything else. That really was a problem.

“But I am happy not to get an injury yet and I am very confident that I have already done the dangerous period. I am ready for the proper fight during the winter period. It is 100 days after the World Cup so I think it is time to raise the game, raise the mentality. It was good for me to retire so I can completely focus on Arsenal and not switch off and on every two or three weeks. Slowly, it is going to start. The season is going to start.”